Digital watermarking is a process for modifying physical or electronic media to embed a machine-readable code into the media. The media may be modified such that the embedded code is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media signals such as images, audio signals, and video signals. However, it may also be applied to other types of media objects, including documents (e.g., through line, word or character shifting), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems typically have two primary components: an encoder that embeds the watermark in a host media signal, and a decoder that detects and reads the embedded watermark from a signal suspected of containing a watermark (a suspect signal). The encoder embeds a watermark by altering the host media signal. The reading component analyzes a suspect signal to detect whether a watermark is present. In applications where the watermark encodes information, the reader extracts this information from the detected watermark.
Several particular watermarking techniques have been developed, and, for robust watermarks, the goal is to design an imperceptible watermark that survives transformation. However, this cannot always be accomplished. The reader is presumed to be familiar with the literature in this field. Particular techniques for embedding and detecting imperceptible watermarks in media signals are detailed in the assignee's co-pending application Ser. No. 09/503,881 (now U.S. Pat. No. 6,614,914) and U.S. Pat. No. 5,862,260, which are hereby incorporated by reference.
The invention provides methods and related systems, devices and software for transmarking media signals. Transmarking relates to converting auxiliary data embedded in a media signal from one digital watermark format to another. It is used in processes that transform the media signal, such as compression, broadcast, editing, rendering, etc., to change the characteristics of the embedded watermark so that the watermark has improved robustness or perceptibility characteristics for its new environment. In some cases, transmarking can be extended to cases where out-of-band data file the header or footer of a media file, or other metadata provided with the media file is transmarked into a watermark or is derived from a watermark. Thus, the watermarks appear to be robust to all transformations.
One aspect of the invention is a method of transmarking a media signal previously embedded with a first digital watermark using a first digital watermark embedding method. This transmarking method detects the first digital watermark in the media signal. It then embeds message information from the first digital watermark into a second digital watermark in the media signal before the media signal undergoes a transformation process. The second digital watermark is adapted to survive the transformation process.
Another aspect of the invention is another method of transmarking a media signal. This method detects the first digital watermark in the media signal, converts the media signal to a different format, and embeds message information from the first digital watermark into a second digital watermark in the converted media signal. The second digital watermark is adapted to robustness or perceptibility parameters associated with the new format.
Further features will become apparent with reference to the following detailed description and accompanying drawings.